Re: problems with NMinimize

*To*: mathgroup at smc.vnet.net*Subject*: [mg109406] Re: problems with NMinimize*From*: Joe Hays <hays.joe at gmail.com>*Date*: Sun, 25 Apr 2010 06:25:55 -0400 (EDT)

I agree with Ingolf. On Sat, Apr 24, 2010 at 4:01 AM, Ingolf Dahl <ingolf.dahl at physics.gu.se>wrote: > Is there any serious Mathematica user in this forum, which has not stumbled > on this problem one or several times, when NMinimize, or some other > function, tries to evaluate a numeric function symbolically first, before > inserting the numbers? Sometimes it would be nice to have an option, > SymbolicEvaluation->False, which could be set for NMinimize in these cases. > It is not always so convenient to have to define an extra function just to > take care of this. I think there is a whole group of commands acting > similarly to NMinimize. > > Ingolf Dahl > Sweden > > > > -----Original Message----- > From: Bob Hanlon [mailto:hanlonr at cox.net] > Sent: den 23 april 2010 09:51 > To: mathgroup at smc.vnet.net > Subject: [mg109376] [mg109370] Re: problems with NMinimize > > > Define a function that only evaluates for numeric arguments > > f[a_?NumericQ, b_?NumericQ] := > Abs[NIntegrate[Sin[x], {x, -a, b}]]^2 > > NMinimize[f[a, b], {a, b}] > > {7.56317*10^-19,{a->0.131888,b->-0.131888}} > > > Bob Hanlon > > ---- Neil Broderick <ngb at ecs.soton.ac.uk> wrote: > > ============= > Hi, > I am trying to use NMinimize to find the solutions to various numerical > equations and I keep getting error > messages concerning non-numerical values. For example consider the > following: > > In[2]:= NMinimize[Abs[NIntegrate[Sin[x], {x, -a, b}]]^2, {a, b}] > > During evaluation of In[2]:= NIntegrate::nlim: x = -1. a is not a valid > limit of integration. >> > > During evaluation of In[2]:= NIntegrate::nlim: x = -1. a is not a valid > limit of integration. >> > > During evaluation of In[2]:= NIntegrate::nlim: x = -1. a is not a valid > limit of integration. >> > > During evaluation of In[2]:= General::stop: Further output of > NIntegrate::nlim will be suppressed during this calculation. >> > > Out[2]= {5.08978*10^-24, {a -> 0.0994414, b -> 0.0994414}} > > My actual problem involves taking Fourier transforms of lists of numbers > but > you get the picture. Why is > NMinimize putting variables into the function rather than just numbers and > is the likely to cause a problem > in some cases? > > regards, > Neil= > >